Dew point! Dew point! Dew point!
It's all about the local temperature and local moisture concentration of the air. Since this field had just been turned and planted it may be releasing a small amount of moisture near that ground that then dissipates. Since there is a higher level of moisture concentration this raises the dew point above what the more macro local environs is. Abbracadabra! Localized Fog! As the moisture dissipates into the local surroundings, the dew point is lowered and Tah Dah! No Fog! Really not all that weird with a basic understanding of thermodynamics.
